Abstract: Curved nickel-titanium (NiTi) orthodontic archwires are widely used in deep bite and open bite correction because of their extraordinary properties of shape memory and superelasticity. The aim of this study were to investigate the mechanical properties of curved NiTi archwires prepared by two different techniques; cold bending and direct electric resistance heat treatment (DERHT) bending and compare those properties to preformed curve NiTi archwires. Preformed curve archwires, 0.016x0.022 inch, were served as a control (group1). Plain archwires were curved into similar geometry as control by fingers (group2) and under the application of DERHT (group3). The three-point bending test was performed to analyze unloading force, springback and stiffness of archwires. Surface hardness was measured by Vickers micro-hardness test. The result showed that the unload force of all sample groups were similar. However, the stiffness and spring back properties of group2 and group3 were significantly higher than those of group 1(p<0.05). Moreover, surface hardness of cold forming technique and preform-curved NiTi archwire was slightly lower than those obtained from DERHT bending technique. Based on these results, the cold bending technique could provide the curved archwire with similar mechanical properties to the preform-curved NiTi archwire. Therefore, the cold bending technique was acceptable to be used as a chair-side orthodontic NiTi wire bending.
Abstract: With the recent advancements in arthroscopic surgery, the use of suture anchor has increased in the surgical treatment of rotator cuff tears. In the present study, we developed a suture anchor system for ligament reconstruction that can be applied to patients with osteoporosis or with low bone density. The anchor screws are made of biocomposites containing poly-L-lactic-co-glycolic acid (PLGA) and beta-tricalcium phosphate (β-TCP) in a 70:30 ratio. The suture anchor system consisted of medial and lateral screw. The lateral screw was designed in a hemicylindrical structure to prevent bone damage. The performance of the developed anchor screw was found to be greater than 402.5 N in a pull-out test.
Abstract: This study investigated four commercially available NiTi orthodontic archwires from different manufactures for their grain structure and surface roughness.Four commercially available pre-formed NiTi orthodontic archwire (Ormco, Sentalloy, Highland and NIC) with diameter 0.016 x 0.022 inch2 were tested. The wire samples were polished and etched to evaluate the morphology and structure of wire surface. Each NiTi archwire was investigated under a reflected light microscope of an Optical Microscope to analyze its grain structure and size, in longitudinal surfaces. The surfaces of wire were qualitatively examined in the secondary electron mode at common magnification (500X). The surface roughness was also evaluated by a surface roughness tester. The descriptive statistic was evaluated the mean and standard deviation of surface roughness and Medcale T-Test was to test the mean difference of the surface roughness in each brands. This study showed an average grain size of 2-8 μm for each NiTi archwire. The wire surface of Ormco and Highland showed straiations along the longitudinal axes, however Sentalloy and NIC showed small pores on the wire surface. The surface roughness was 0.09 μm for Highland, 0.25 μm for Sentalloy, 0.28 μm for Ormco and 0.46 μm for NIC archwire. The Highland was smoothest and NIC was the roughest. There were in significant (p < 0.05) difference of surface roughness of each brands. The results showed that the four manufactures NiTi archwires were different in grain size, wire surface and surface roughness. During clinical application, these archwires may exhibit different mechanical properties, such as strength, hardness, ductity, and friction because of their microstructure.
Abstract: In this study, mechanical properties development of reinforcing bar steel (rebar) has examined through heat treatment process. This rebar was made from low carbon lateritic steel with the small amount of alloying elements Cr,Mn and Ni. There were 4 rebar steel samples that consisted of rebar steel was applied hot rolled at 1200 °C at the beginning process in factory (sample A) and three others were conducted by quenching (sample B, C and D). The various of cooling media such as water (sample B), oil (sample C) and air (sample D) have applied to obtain different microstructure behavior and also mechanical properties. Initial heating was conducted to B,C and D rebar specimens at the austenitizing temperature (950 °C) for 1 h and followed by quenching. The experimental results showed that water quench exhibited of higher hardness level (50,26 HRC) for rebar steel but decreasing in toughness (34 Joule) and elongation (4%) than as cast because of martensite phase formed. Sample C showed that martensite and the small amount of retained austenite with hardness and tensile strength below the sample B, but elongation and energy absorbed were above. The lowest of hardness and tensile strength were obtained from sample D. It was appropriate with microstructuree formed as follows ferrite-pearlite phase and widmanstatten-bainite cluster. Nevertheless, sample D is suitable treatment for tensile strength and elongation requirements rebar standard, there are 558 Mpa and 26% respectively (min. 440 MPa and 20%).
Abstract: The use of industrial by-products could provide a feasible solutions for the construction industry to reduce the strain on supply of natural aggregate as well as achieving the concept of environmentally friendly binder material by replacing part of Portland cement. This paper reports the results of an experimental study, mainly on the permeability and porosity characteristic of pervious concrete developed by substituting 26% Portland cement with air-cooled blast furnace slag and replacing part of natural coarse aggregate with granular blast furnace slag of different aggregate size and different water/cement ratio. The pervious concrete with lower water cement ratio and 25% GBFS affected either the porosity or the compressive strength of the pervious concrete. As expected, the porosity increased in pervious concrete with bigger aggregate size, but decreased when the smaller aggregate size was used. Partial substitution of coarse aggregate with granular GBFS of the same gradation size did not affect the permeability coefficient. Specimens developed using water cement ratio of 0.34 and coarser aggregate size tend to have a greater water permebility compared with those of 0.3 water/cement ratio.
Abstract: Pervious concrete primarily is used as a means of storm water management. Taking into consideration the environment issues, the binder can also be formed by partially replaced Portland cement by cementitious materials, such as blast furnace slag fine powder, fly ash and silica fume. The combination of the binder materials was determined based on previous work, which composed of 56% Portland Composite Cement, 15% fly ash Type F, 26% air-cooled blast furnace slag from a local steel Industry and 3% condensed silica fume. The compressive strength of specimens with coarser aggregate was lower compared with the control pervious concrete, but still within the range of the requirement compressive strength according to ACI 522R-2010. The difference of the aggregate size affected the enhancement of the compressive strength. The flexural strength of pervious concrete with aggregate size of 9.5mm-12.5mm tend to be higher compared with that of pervious concrete with smaller aggregate size. Furthermore, the addition of 6% natural fine aggregate while applying higher water/cement ratio could be a contribution to the enhancement of the compressive and the flexural strength.
Abstract: Carbon nanotube (CNT) acts as electromagnetic interference shielding material in concrete composites was presented in this paper. Three concrete samples respectively with different CNT contents were casted and experimentally tested their shielding effectiveness (SE). The SE measurements which were obtained in function of frequency were taken using vector network analyzer (VNA) in the frequency range of 2.4 - 4.0 GHz. The experimental results showed that the CNT contributes to change in conductivity due to the positioning of the electric field of the incident wave and thus, produces different shielding performances. The EMI SE of concrete composites is improved up to 41dB with CNT concentration of 1.5-2.0 wt%.
Abstract: Sandwich composite materials are widely used in various applications, due to their advanced flexibility in responding to special design requirements. This paper presents the evaluation of thick sandwiches, aimed to be imbedded in platforms of a green energy unit, accommodating storage water tanks. The evaluation of the damage tolerance was made having in view previous studies on similar materials and covered assessment of results obtained during low velocity impact tests and post-impact tests, aimed to establish the residual mechanical performance. Ways to increase the damage tolerance, by diminishing the invasive effect of low velocity impact, were also explored.